On an aircraft, such as a rotorcraft (e.g., a helicopter), conducting an inspection or maintenance activity with respect to a drive shaft is laborious and time consuming. For example, various visual inspections are required at fixed intervals, often requiring a complete removal of the drive shafts and couplings. After removal, frequent bolt-nut torque checks must be performed. Considering that this process must be performed for each of the drive shaft sections in the aircraft, the maintenance burden is substantial. However, experience indicates that a majority of these inspections do not uncover any problems, resulting in tremendous inefficiencies.
Mechanical failure modes typically looked for or examined during these inspections include cracking of a disc coupling, buckling of the disc coupling, bolt-hole elongation (e.g., elongation in flanges), corrosion, damage, security, wear, lamination spread, and loss of bolt preload. It is difficult to detect and quantify the severity (e.g., in terms of likelihood of losing complete torque carrying capacity) of each of these failure modes.